1. Field of the Invention
Efforts to expand world markets for U.S. farm products have led to the investigation of marketing commodities in a higher-valued, more finished form than is now customary. Defatted corn germ flour, a byproduct of the corn oil industry, is one such commodity having nutritional and economic potential. Traditionally, it has been utilized as an ingredient in animal feeds. The principal problem in developing corn germ as a finished vegetable protein product for human consumption relates to product deterioration during shipment, distribution and other extended periods of storage. Conventional pressing methods and solvent extraction methods using hexane or similar hydrocarbons leave lipids in the flour which either auto- or enzymatically oxidize into compounds which contribute to grassy/beany and bitter flavors. The commercially produced, solvent-extracted, corn germ flour taught by Canolty et al. [J. Food Sci. 42: 269 (1977)], for example, contains a residual oil content of 2%. The result is an eventual reduction in the product's organoleptic and nutritional qualities. Attempts to inactivate the oxidative enzymes by toasting have proven unsatisfactory from the standpoint of effectiveness, economics, and energy consumption. This invention relates to a method of processing corn germ so as to extract the oil and simultaneously produce a high-quality, food-grade flour without toasting.
2. Description of the Prior Art
In the art of vegetable oil extraction, increasing attention has been given to the technology of supercritical fluids as an alternative to current extraction methods. Supercritical fluids (SCF's) are often referred to as dense gases. Technically, an SCF is a gas existing above its critical temperature and critical pressure, as defined in the phase diagram of the pure substance. When a gas is compressed above its critical temperature, densities increase dramatically. Therefore, under a given set of conditions, an SCF may possess the density of a liquid while maintaining the diffusivity of a gas. Of the several SCF's investigated, supercritical carbon dioxide (SC-CO.sub.2) is ideal because it is nontoxic, nonexplosive, inexpensive, readily available, and easily removed from the extracted product.
The solvent properties of SCF's have been recognized for over 100 years, but commercial applications have been slow in developing. Decaffeination of coffee with SC-CO.sub.2 is the only current large-scale commercial SCF process, though other uses are being investigated. British Pat. No. 1,356,749 teaches the SCF extraction of oils from crushed or coarsely ground seeds including copra, sunflower, coconut, soybeans, and peanuts. Stahl et al. [J. Agric. Food Chem., 28(6): 1153-1157 (1980)] elaborates on the parameters influencing the removal and fractionation of soybean, sunflower seed, and rapeseed oils in terms of yield, color, taste, and odor. As exemplified by these and other teachings in the art, applications of SCF technology have emphasized the oil recovery, with little or no attention being given to the seed residue. An exception is found in the disclosure of Schwengers, U.S. Pat. No. 3,939,281. After SCF extraction of crushed whole cereal grains, Schwengers soaks the defatted residue in aqueous sulfur dioxide and optionally removes fractions of gluten and starch. The remainder of the residue is recovered for use as animal fodder.